The present invention relates to a toner for the development of an electrostatic image, particularly for use in electrophotographic process copying machines and printers. More particularly, the present invention relates to a toner for the development of an electrostatic image prepared by emulsion polymerization agglomeration method.
A conventional toner for the development of an electrostatic image which has previously been widely used in electrophotography has been prepared by a process which comprises melt-kneading a mixture of a binder resin such as of a syrene-acrylate copolymer, or polyester, a colorant such as carbon black and a pigment, a charge control agent and/or a magnetic material through an extruder, grinding the material obtained, and then classifying the resulting powder. However, the conventional toner obtained by such a melt-kneading/grinding process has the disadvantage that the controllability of the particle diameter of the toner is limited, making it difficult to prepare a toner substantially having an average particle diameter of not more than 10 xcexcm, particularly not more than 8 xcexcm in a good yield. Thus, the conventional toner cannot be considered good enough to provide the high resolution that will be required in the future electrophotography.
In order to achieve oilless low temperature fixability, an approach involving the blend of a low softening wax in a toner during kneading has been proposed. In the kneading/crushing process, however, the amount of wax to be blended is limited to about 5% by weight. Thus, toners having sufficient low temperature fixability and OHP transparency cannot be obtained.
In an attempt to overcome difficulty in controlling the particle diameter and hence realize high resolution, JP-A-63-186253 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) proposes a process for the preparation of a toner involving emulsion polymerization/agglomeration process. However, this process is also limited in the amount of wax that can be effectively introduced into the agglomeration step. Thus, this process leaves something to be desired in the improvement in oilless low temperature fixability.
JP-A-9-190012 proposes a process for the preparation of a toner involving emulsion polymerization/agglomeration process using crosslinked primary polymer particles for suppressing gloss in a formed image. However, this process provides an image with insufficient OHP transparency.
In JP-A-8-50368, a toner is disclosed containing a low melting point ester-based wax. Specifically, however, the toner described in this publication is produced by suspension polymerization. The particle size distribution of the toner is difficult to control due to the production process. Thus, it is difficult to obtain a high resolution image with this toner. In JP-A-10-301322 a toner is disclosed containing a low melting point ester-based wax produced by an emulsion polymerization agglomeration process. The toner described in this publication, however, comprises an uncrosslinked binder resin. Further, OHP transparency and offset resistance of the toner are not sufficient.
It is therefore an object of the present invention to overcome the difficulties of the conventional toner for the development of an electrostatic image.
It is a further object of the present invention to provide a toner having high resolution, oilless fixability, and sufficient low temperature fixability, offset resistance, blocking resistance, fixing temperature width and OHP transparency.
It is a further object of the present invention to provide a process for producing such a toner. These and other objects of the present invention have been satisfied by the discovery of an emulsion polymerization agglomeration toner comprising a low melting point wax and using primary polymer particles and/or particulate resin having a specified crosslinking degree, and the process for producing the same.
The present invention relates to a toner or the development of an electrostatic image comprising an agglomerate of particles obtained by agglomerating a mixture comprising (i.e. at least) primary polymer particles and primary colorant particles, wherein an insoluble content in tetrahydrofuran (the THF insoluble content) of the toner is from 15% to 80 w/w (all percentages are w/w % unless otherwise indicated) and the toner comprises wax having a melting point of 30 to 100xc2x0 C.
The present invention further relates to a toner for the development of an electrostatic image comprising an agglomerate of particles obtained by agglomerating at least primary polymer particles and primary colorant particles, wherein the THF insoluble content of the primary polymer particles is from 15% to 70 w/w % and the toner comprises wax having a melting point of 30 to 100xc2x0 C.
A further embodiment of the present invention relates to a toner for the development of an electrostatic image comprising an agglomerate of particles obtained by agglomerating at least primary polymer particles and primary colorant particles, wherein a proportion of a polyfunctional monomer in monomer components constituting the primary polymer particles is 0.005 to 5 w/w % and the toner comprises wax having a melting point of 30 to 100xc2x0 C.
An additional embodiment of the present invention relates to a method for producing a toner for the development of an electrostatic image comprising agglomerating at least primary polymer particles and primary colorant particles to form an agglomerate of particles, wherein the primary polymer particles are produced by emulsion polymerization of a monomer mixture comprising 0.005 to 5 w/w % of a polyfunctional monomer, and the toner comprises wax having a melting point of 30 to 100xc2x0 C.
The toner according to the present invention comprises wax, primary polymer particles and primary colorant particles, and, if necessary, comprises one or more of a charge control agent, particulate resin and other additives. The toner of the present invention is produced by an emulsion polymerization agglomeration method. According to the emulsion polymerization agglomeration method, the toner is produced by co-agglomerating at least primary polymer particles obtained by emulsion polymerization, and primary colorant particles and, depending upon necessity, primary charge control agent particles and particulate resin.
Further, in the toner of the present invention the resin constituting primary polymer particles and/or particulate resin is preferably crosslinked and a low melting point wax is preferably included in the toner.
The wax used in the present invention, can be any conventional wax having a melting point of 30 to 100xc2x0 C. Examples of such waxes include olefinic waxes such as low molecular weight polyethylene, low molecular weight polypropylene and polyethylene copolymer; paraffin waxes; ester-based waxes having a long-chain aliphatic group such as behenyl behenate, montanic acid ester and stearyl stearate; vegetable waxes such as hydrogenated castor oil and carnauba wax; ketones having a long-chain alkyl group such as distearyl ketone; silicones having an alkyl group; higher aliphatic acids such as stearic acid; long-chain aliphatic alcohols such as eicosanol; carboxylic acid esters of polyhydric alcohols such as glycerol and pentaerythritol, and long chain aliphatic acids or partial esters thereof; and higher aliphatic acid amides such as oleic acid amide and stearic acid amide; and low molecular polyesters.
Among these waxes, those having a melting point of not less than 40xc2x0 C. are preferred, with a melting point of not less than 50xc2x0 C. being more preferred to improve the fixability of the toner. Further, it is preferred that the wax have a melting point of not higher than 90xc2x0 C., more preferably not higher than 80xc2x0 C. If the melting point of wax is too low, the wax may be exposed on the surface of the toner after fixing, which is liable to produce a sticky feel. On the contrary, if the melting point is too high, the toner can be deteriorated in fixability at a low temperature.
As the wax compound, an ester-based wax obtained from an aliphatic carboxylic acid and a monovalent or polyvalent alcohol is preferably used. The alcohol used may be an aliphatic alcohol. Among ester-based waxes, those having 20 to 100 carbon atoms are more preferable and those having 30 to 60 carbon atoms are particularly preferable.
Among esters of a monovalent alcohol and an aliphatic carboxylic acid, behenyl behenate and stearyl stearate are most preferred. Among esters of a polyvalent alcohol and an aliphatic carboxylic acid, stearic acid ester of pentaerythritol and the partial ester thereof, montanic acid ester of glycerol and the partial ester thereof are most preferred.
The above-described waxes can be used alone or in any mixture thereof. Further depending upon the fixing temperature of the toner, the melting point of a wax compound can be optionally selected. In the context of the present invention the term xe2x80x9cwaxxe2x80x9d can refer to a single wax compound or a mixture of wax compounds.
For the purpose of enhancing fixability, a mixture of two or more, preferably three or more wax compounds is particularly effective. In particular, it is preferable that three or more wax compounds are used together and that formulation amounts of respective compounds preferably do not exceed 60 w/w %, more preferably 45 w/w % and most preferably 40 w/w %, of the entire wax.
When using mixtures of wax compounds, it is preferable that at least one of the waxes is the above-described carboxylic acid ester of a monovalent or polyvalent alcohol. In another embodiment, at least two wax compounds are aliphatic alcohol esters of an aliphatic carboxylic acid having 20 to 100 carbon atoms. The wax compound present in the highest amount is more preferably an alkanoic acid ester of a monovalent or a polyvalent alcohol, most preferably an alkyl ester of an alkanoic acid. In the case where the most abundant wax compound is an alkyl ester of an alkanoic acid, the second most abundant wax compound is preferably a different alkyl ester of an alkanoic acid or alkanoic acid ester of a polyvalent alcohol.
Mixtures of wax compounds more preferably contain 4 or more wax compounds, most preferably 5 or more wax compounds. The upper limit of wax compounds in the mixture is not particularly limited. However, in view of production, it is preferably 50 different wax compounds or less.
If at least three kinds of wax compounds are present, the sum of the two most abundant wax compounds is preferably 88% or less, more preferably 85% or less, and particularly preferably 80% or less.
The wax compound most abundant in the mixture preferably has a melting point of 40xc2x0 C. or more, more preferably 50xc2x0 C. or more. Further, the wax compound most abundant in the mixture preferably has a melting point of 90xc2x0 C. or less, more preferably 80xc2x0 C. or less. Further, particularly preferably, the two most abundant wax compounds each have a melting point of 40xc2x0 C. to 90xc2x0 C.
In the present invention, the wax is used as an emulsion (particulate wax) by dispersing the same in the presence of an emulsifier.
The emulsion is used for seed polymerization of monomer. Specifically, it is used for the formation of particulate resin or primary polymer particles comprising wax encapsulated therein. Alternatively, the wax is incorporated in a toner by co-agglomerating emulsion and latex (dispersion of primary polymer particles).
Particulate wax to be used in the present invention is obtained by emulsifying the above-described wax in the presence of at least one emulsifier selected from known cationic surfactant, anionic surfactant or nonionic surfactant. Two or more kinds of these surfactants can be used together.
The wax used in the present invention has a melting point of 30 to 100xc2x0 C. Thus, since the wax has a melting point of less than the boiling point of water, where the dispersion of wax particles is prepared by emulsifying the wax, the wax is preferably dispersed and emulsified in a molten state i.e. by heating a mixture of wax, water and emulsifier to the temperature of the melting point of the wax or more. The particulate wax may be produced by dispersing one or more wax compounds in water having a temperature higher than a melting temperature of the particulate wax, in the presence of an emulsifier.
Specific examples of suitable cationic surfactants include dodecyl ammonium chloride, dodecyl ammonium bromide, dodecyl trimethyl ammonium bromide, dodecyl pyridinium chloride, dodecyl pyridinium bromide, and hexadecyl trimethyl ammonium bromide.
Specific examples of suitable anionic surfactants include aliphatic soap such as sodium stearate and sodium dodecanate, sodium dodecyl sulfate,sodium dodecylbenzenesulfonate, and sodium laurylsulfate.
Specific examples of suitable nonionic surfactants include polyoxyethylenedodecyl ether, polyoxyethylenehexadecyl ether, polyoxyethylenenonylphenyl ether, polyoxyethylenelauryl ether, polyoxyethylene sorbitan monoleate ether, and monodecanoyl succrose.
Among these surfactants, an alkali metal salt of a straight chain alkylbenzene sulfonic acid is preferable. The volume-average particle diameter of the particulate wax is preferably from 0.01 xcexcm to 3 xcexcm, more preferably from 0.1 xcexcm to 2 xcexcm, and particularly from 0.3 to 1.5 xcexcm. For the measurement of average particle diameter, LA-500 produced by Horiba Co., Ltd. may be used. If the average particle diameter of the particulate wax exceeds 3 xcexcm, the polymer particles obtained by seed polymerization can be too large to produce a high resolution toner. On the contrary, if the average particle diameter of the emulsion falls below 0.01 xcexcm, it may be difficult to prepare the dispersion thereof.
One feature of the present invention resides in the use of a crosslinked resin as the resin constituting the primary polymer particles and/or the particulate resin, as described below.
The primary polymer particles used in the present invention are obtained by emulsion polymerization of a monomer mixture. In the emulsion polymerization, particulate wax can be used as seed, which is desirable in view of dispersibility of the wax in the toner.
In order to effect seed emulsion polymerization, a monomer having a Brxc3x6nsted acidic group (hereinafter, referred to as simply an acidic group) or a monomer having a Brxc3x6nsted basic group (hereinafter, referred to as simply a basic group) and a monomer having neither a Brxc3x6nsted acidic group nor a Brxc3x6nsted basic group (hereinafter, also referred to as other monomer) are successively added to cause polymerization in the emulsion containing particulate wax. During this procedure, these monomers may be added separately or concurrently in any combination. Alternatively, a plurality of monomers may be previously mixed before being added. Further, the composition of monomers to be added may be changed during addition. Moreover, these monomers may be added as they are or in the form of an emulsion obtained by mixing with water and/or a surfactant. As such a surfactant, one or more of the exemplified surfactants may be used.
During the seed emulsion polymerization process, an emulsifier (a surface active agent) may be added to the wax emulsion in a predetermined amount. A polymerization initiator may be added before, at the same time with or after the addition of the monomers. These addition methods may be employed in combination.
Examples of the monomer having a Brxc3x6nsted acidic group usable in the present invention include monomers having a carboxylic group such as acrylic acid, methacrylic acid, maleic acid, fumaric acid and cinnamic acid, monomers having a sulfonic group such as styrene sulfonate, and monomers having a sulfonic amide group such as vinyl benzene sulfonamide.
Particularly preferred monomers for the primary particles are acrylic acid and/or methacrylic acid, with or without other comonomers.
Examples of the monomer having a Brxc3x6nsted basic group include aromatic vinyl compounds having an amino group such as aminostyrene; monomers containing a nitrogen-containing heterocycle such as vinylpyridine and vinylpyrrolidone; and (meth)acrylic acid esters having an amino group such as dimethylaminoethyl acrylate and diethylaminoethyl methacrylate.
Further, these monomers having an acidic group and monomers having a basic group can be present as salts with respective counter ions.
The amount of monomer having a Brxc3x6nsted acidic group or a Brxc3x6nsted basic group in a monomer mixture used to prepare the primary polymer particles is preferably 0.05% by weight or more, more preferably 0.5% by weight or more, and most preferably 1% by weight or more. Further, the amount of monomers having an acidic or basic group is preferably 10% by weight or less, more preferably 5% by weight or less. The amount of monomer having a Brxc3x6nsted acidic group or a Brxc3x6nsted basic group in the monomer mixture used to prepare the primary polymer particles can be in a range of from 0.5% by weight to 5% by weight.
Examples of the other comonomers used herein include styrenes such as styrene, methylstyrene, chlorostyrene, dichlorostyrene, p-tert-butylstyrene, p-n-butylstyrene and p-n-nonylstyrene; and (meth)acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, hydroxyethyl acrylate, ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, hydroxyethyl methacrylate and ethylhexyl methacrylate; acrylamide, N-propylacrylamide, N,N-dimethylacrylamide, N,N-dipropylacrylamide, N,N-dibutylacrylamide, and acrylic amide. Particularly preferred among these monomers are styrene, butyl acrylate.
Where a crosslinked resin is used as the primary polymer particles, as a crosslinking agent to be used together with the above-described monomers, radically polymerizable polyfunctional monomers can be used. However, it is possible to produce primary polymer particles from a monomer mixture substantially free of a polyfunctional monomer. Examples of such radically polymerizable polyfunctional monomers include divinyl benzene, hexanediol diacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, neopentyl glycol dimethacrylate, neopentyl glycol diacrylate and diallyl phthalate. Further, monomers having a reactive group in a pendant group, such as glycidyl methacrylate, methylol acrylamide and acrolein can be used.
Preferably, radically-polymerizable bifunctional monomers, more preferably, divinyl benzene and hexanediol diacrylate are desirably used.
The amount of such a polyfunctional monomer used in the monomer mixture is preferably 0.005% by weight or more, more preferably 0.01% by weight or more and particularly preferably 0.05% by weight or more. Further, the amount of polyfunctional monomer is preferably 5% by weight or less, more preferably 3% by weight or less, and particularly preferably 1% by weight or less.
The polyfunctional monomers may be used singly or in admixture, and are preferably added such that the resulting polymer exhibits a glass transition temperature of from 40xc2x0 C. to 80xc2x0 C. If the glass transition temperature of the polymer exceeds 80xc2x0 C., the resulting toner exhibits too high a fixing temperature. Further, the toner may have a decreased OHP transparency. On the contrary, if the glass transition temperature of the polymer falls below 40xc2x0 C., the storage stability of the toner deteriorates.
Examples of polymerization initiators that can be used include, but are not limited to, persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate; redox initiators obtained by combining these persulfates as one component with reducing agents such as acidic sodium sulfite; water-soluble polymerization initiators such as hydrogen peroxide,4,4xe2x80x2-azobiscyanovaleric acid, t-butyl hydroperoxide and cumene hydroperoxide; redox initiators obtained by combining these water-soluble polymerization initiators as one component with reducing agents such as ferrous salt; benzoyl peroxide, and 2,2xe2x80x2-azobis-isobutylonitrile. These polymerization initiators may be added before, at the same time with or after the addition of the monomers. These addition methods may also be employed in combination.
In the present invention, any known chain transfer agent may be used, as desired. Suitable examples of chain transfer agents include, but are not limited to, t-dodecyl mercaptan, 2-mercaptoethanol, diisopropyl xanthogen, carbon tetrachloride, and bromotrichloromethane. These chain transfer agents may be used singly or in combination. The chain transfer agents may be used in an amount of from 0 to 5% by weight based on the weight of the polymerizable monomers used.
The primary polymer particles obtained as described above have a wax substantially encapsulated therein. The primary polymer particles can have any desired morphology, such as, core-shell type, phase separation type, occlusion type or combinations or mixtures thereof. A particularly preferred morphology is a core-shell type particle. Components other than wax, such as a pigment and a charge control agent, can be further used as seed so far as they don""t depart from the scope of the present invention. Further, a colorant and a charge control agent dissolved or dispersed in wax can be used.
The volume-average particle diameter of the primary polymer particles can be any size, but is generally from 0.02 to 3 xcexcm, preferably from 0.05 to 3 xcexcm, more preferably from 0.1 to 2 xcexcm and most preferably 0.1 to 1 xcexcm. For the measurement of volume average particle diameter, for example, UPA (Ultra Particle Analyzer produced by Nikkiso Co., Ltd.) may be used. If the particle diameter is less than 0.02 xcexcm, the agglomeration rate can be difficult to controlled. If the particle diameter exceeds 3 xcexcm, the toner obtained by agglomeration may have too large a particle diameter to provide a high resolution toner.
In the present invention, primary polymer particles are agglomerated to form an agglomerate of particles. Within the context of the present invention, the agglomerate of particles can take the form of an agglomerate where the individual particles are still distinguishable to a unitary large particle where the individual primary particles have coalesced to the point of no longer being distinguishable and the entire spectrum of species therebetween. However, in a preferable embodiment, a particulate resin (as described below) is further adhered or fixed thereto to form a toner. In such a toner, the primary polymer particles or the particulate resin for coating an agglomerate of primary particles, or both have a THF insoluble portion.
Therefore, in a toner wherein no particulate resin coating is present, a crosslinked resin is preferred as the primary polymer particles. In a toner having a particulate resin coating, at least one of the primary polymer particles or particulate resin comprises a crosslinked resin. A most preferred embodiment is the case wherein both primary polymer particles and particulate resin are crosslinked resins. The THF insoluble content of the primary polymer particles is generally 15 w/w % or more, preferably 20 w/w % or more, more preferably 25 w/w % or more. Additionally, the THF insoluble content is preferably 70% or less.
If the crosslinking degree is too low, offset can occur. Further, if the crosslinking degree is too high, OHP transparency may be decreased.
In the present invention, the THF insoluble content of the primary polymer particles and optionally used particulate resin, is controlled to provide a final toner having a THF insoluble content of from 15 to 80 w/w %.
Among components constituting the primary polymer particles, a THF soluble component preferably has a molecular weight peak (Mp) of 30,000, more preferably 40,000 or more. Further, the Mp is preferably 150,000 or less, more preferably 100,000 or less.
When a crosslinked resin is used, a THF soluble component preferably has a molecular weight peak of 100,000 or less, more preferably 60,000 or less.
When the molecular weight peak is noticeably smaller than the above-described range, the offset property of the toner at high temperature side can be poor. When the molecular weight peak is noticeably larger than the above-described range, the offset property of the toner at low temperature may be deteriorated.
Among components constituting primary polymer particles, those soluble in tetrahydrofuran have a weight-average molecular weight (Mw) of preferably 30,000 or more, more preferably 80,000 or more, a weight-average molecular weight (Mw) of preferably 500,000 or less, more preferably 300,000 or less.
In accordance with the present invention, preferably, primary polymer particles and primary colorant particles are simultaneously agglomerated to form an agglomerate of the particles, to provide a toner or a toner core material. Suitable colorant particles include inorganic or organic pigments and organic dyes, alone or in combination as desired. Specific examples of suitable colorants include known dyes and pigments such as aniline blue, phthalocyanine blue, phthalocyanine green, hansa yellow, rhodamine dye or pigment, chrome yellow, quinacridone, benzidine yellow, rose bengal, triallylmethane dye, monoazo dyes or pigments, disazo dyes or pigments, and condensed azo dyes or pigments. These dyes or pigments may be used singly or in admixture. If the toner of the present invention is a full-color toner, benzidine yellow, monoazo dyes or pigments or condensed azo dyes or pigments are preferably used as a yellow dye or pigment, quinacridone dyes or pigments or monoazo dyes or pigments are preferably used as a magenta dye or pigment, and phthalocyanine blue is preferably used as a cyan dye or pigment. The colorant is normally used in an amount of from 3 to 20 parts by weight based on 100 parts by weight of the binder resin used. In the context of the present invention, the term xe2x80x9cbinder resinxe2x80x9d refers to the total of primary polymer particles and particulate resin (if present).
In one embodiment, a magenta colorant compound represented by the following formulae (I) or (II) is is used in a toner of the present invention having a particulate resin coating. Namely a colorant compound represented by the formula (I) can desirably prepare a primary colorant particle dispersion and, therefore, the resulting toner can have a desirable hue. Since a compound represented by the formula (II) is likely to be positively charged, in the case where it is used for a negatively charged toner, the agglomerate of particles containing the colorant (toner core material) is coated with particulate resin so that the colorant is not exposed. Thus, the toner can be negatively charged. When a compound represented by the formula (I) or (II) is included in a toner obtained by an emulsion polymerization agglomeration method, a desirable magenta hue can be obtained. Thus, the compound represented by the formula (I) or (II) can be especially advantageous as the colorant of the toner of the present invention. 
wherein R1 and R2 each independently represents a hydrogen atom, an alkyl group, an alkyl group having 1 to 8 carbons or a halogen atom, provided that at least one of R1 and R2 is a halogen atom, and M represents Ba, Sr, Mn, Ca or Mg. 
wherein A and B each, independently, represent an aromatic ring which can be substituted, and R3 represents a hydrogen atom, a halogen atom, a nitro group, a cyano group, a hydrocarbon group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, an aminosulfonyl group wherein the nitrogen atom may be substituted or an aminocarbonyl group wherein the nitrogen atom may be substituted.
In the general formula (II), A and B preferably represent a benzene ring or a naphthalene ring. Among compounds represented by formula (II), those represented by the following formula (IIa) are more preferred: 
wherein R3 to R6 each independently represents a hydrogen atom, a halogen atom, a nitro group, a cyano group, a hydrocarbon group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, an aminosulfonyl group wherein the nitrogen atom may be substituted or an aminocarbonyl group wherein the nitrogen atom may be substituted.
In the formula (IIa), the nitrogen atom of the aminosulfonyl group or aminocarbonyl group, can be substituted with an alkyl group, an aryl group, an alkoxyalkyl group, a haloalkyl group or a haloaryl group.
Further, a compound wherein R3 is a hydrogen atom, R4 is a methoxy group, R5 is a hydrogen atom and R6 is a chlorine atom is the most preferable in view of spectral reflectance, dispersibility in a polymerizable monomer and a processability to a colorant dispersion.
In the case where these colorants are used by emulsifying in water in the presence of an emulsifier to form an emulsion, those having a volume-average particle diameter of 0.01 to 3 xcexcm are preferably used.
In the present invention, a charge control agent can be included in the toner if desired. The charge control agent can be incorporated into the toner, preferably by a method wherein the charge control agent is used as seed together with wax in obtaining primary polymer particles, a method wherein the charge control agent is used by dissolving or dispersing in monomer or wax, or a method wherein primary polymer particles and primary charge control agent particles are agglomerated at the same time to form an agglomerate of particles, which is used as a toner. However, a preferable method comprises adhering or fixing a charge control particle before, during or after the process for adhering or fixing particulate resin. In this case, it is preferable that the charge control agent is also used as an emulsion in water having an average particle diameter of from 0.01 to 3 xcexcm (primary charge control agent particles).
At least a substantial portion of the agglomerate particles which contains at least primary polymer particles and primary colorant particles is coated with the particulate charge control agent. Any conventional charge control agent can be used alone or in combination of two or more. For example, a quaternary ammonium salt, and a basic electron-donating metal material are preferably used as a positively-charging charge control agent, and a metal chelate, a metal salt of an organic acid, a metal-containing dye, nigrosine dye, an amide group-containing compound, a phenol compound, naphthol compound and the metal salts thereof, an urethane bond-containing compound, and an acidic or an electron-attractive organic substance are preferably used as a negatively-charging charge control agent.
Taking into account adaptability to color toner (the charge control agent itself is colorless or has a light color and hence doesn""t impair the color tone of a toner), a quaternary ammonium salt compound is preferably used as a positively-charging charge control agent and a metal salt or metal complex of salicylic acid or alkylsalicylic acid with chromium, zinc or aluminum, a metal salt or metal complex of benzylic acid, amide compound, phenol compound, naphthol compound, phenolamide compound, and hydroxynaphthalene compound such as 4,4,xe2x80x2-methylenebis[2-[N-(4-chlorophenyl)amide]-3-hydroxynaphthalene are preferably used as a negatively-charging charge control agent. The amount of the charge control agent to be used may be determined by the required charged amount of toner. In practice, however, it is normally from 0.01 to 10 parts by weight, preferably from 0.1 to 10 parts by weight, based on 100 parts by weight of the binder resin used.
In the toner of the present invention, if desired, particulate resin can be coated (adhered or fixed) over the above-described agglomerate of particles to form toner particles.
The particulate resin is preferably used as an emulsion obtained by dispersing the same with an emulsifier (the above-described surface active agent) in water or a liquid mainly comprising water. The particulate resin used in the outermost layer of the toner is preferably substantially free from wax, more preferably containing  less than 1% wax by weight of particulate resin.
Preferred particulate resins, include those having a volume-average particle diameter of 0.02 to 3 xcexcm, more preferably 0.05 to 1.5 xcexcm. The particulate resin can comprise units obtained from the same monomers used to prepare the primary polymer particles or can use different monomers from those used in the primary particles.
When the toner is prepared by coating an agglomerate of particles with particulate resin, the particulate resin is preferably a crosslinked resin. In the present invention, it is most preferred that at least one of the primary polymer particles or particulate resin be crosslinked. As the crosslinking agent, the polyfunctional monomers used for the primary polymer particles can be used.
When the particulate resin is a crosslinked resin, the crosslinking degree is normally 5 w/w % or more, preferably 10 w/w % or more and more preferably 15 w/w % or more, based on measurements of THF insoluble content. More preferably, the particulate resin has a THF insoluble content of 70 w/w % or less. In order to achieve the above-described preferable range of THF insoluble content, the formulation amount of polyfunctional monomer is preferably 0.005% by weight or more, more preferably 0.01% or more and most preferably 0.05% or more, based on total monomer mixture used for preparing the particulate resin. Further, the amount of polyfunctional monomer is preferably 5% by weight or less, more preferably 3% by weight or less, and most preferably 1% by weight or less, based on total monomer mixture.
Among components of the particulate resin, a molecular peak (Mp) of THF-soluble components is preferably 30,000 or more, more preferably 40,000 or more, and is preferably 150,000 or less, more preferably 100,000 or less.
Particularly, in the case where a crosslinked resin is used, a molecular peak (Mp) of THF-soluble components is preferably 100,000 or less, more preferably 60,000 or less.
Among components of the particulate resin, a weight-average molecular weight (Mw) of THF-soluble components is preferably 30,000 or more, more preferably 50,000 or more, preferably 500,000 or less, more preferably 300,000 or less.
When the toner is coated with a particulate resin, however, the resulting toner can have a core-shell construction (with the primary polymer particles and colorant particles agglomerated in the core and the particulate resin coated on the outside) or it is also possible the during the aging of the toner with the particulate resin present, there is migration of particulate resin into the agglomerate with concomitant migration of the primary polymer particles and/or colorant particles into the outside coating layer. This can result in the outer layer containing slight amounts of primary polymer particles and colorant particles or even in the extreme, in a toner that is homogeneous with respect to primary polymer particles, colorant particles and particulate resin. All embodiments between distinct layers and homogeneous toner are included in the present invention.
In the case where the toner is a negatively charged toner, it is preferred to have the agglomerate coated with the particulate resin. If aging of the particulate resin coated agglomerate results in mixing to the point wherein no boundary exists between the agglomerate and the particulate resin, it is further preferred to provide an outer layer of particulate resin only.
Additionally, even when there is a distinct layer on the agglomerated primary polymer particles and colorant particles, the layer can completely cover the agglomerate or can be on a substantial portion, either continuously or non-continuously. Preferably, the particulate resin forms a coating on at least 75% of the surface area of the agglomerate, more preferably at least 85%, even more preferably at least 95%. Most preferably is a complete covering of the agglomerate with the particulate resin.
In a preferred embodiment of the present invention, the above-described primary polymer particles, primary colorant particles, and optionally particulate charge control agent, particulate wax and other additives are emulsified to form an emulsified liquid, which are co-agglomerated to form an agglomerate of particles. Among respective components to be agglomerated, the charge control agent dispersion, particulate wax or other additives can be added during the agglomeration process or after the agglomeration process.
Embodiments of the agglomeration process include 1) methods wherein agglomeration is effected by heating, and 2) methods wherein agglomeration is effected chemically, such as by addition of an electrolyte.
In the case where agglomeration is effected by heating, the agglomeration temperature is preferably in a range of from 5xc2x0 C. to Tg (Tg is the glass transition temperature of primary polymer particles), more preferably a range of from (Tgxe2x88x9210xc2x0 C.) to (Tgxe2x88x925xc2x0 C.). By employing this preferred temperature range, a desirable toner particle diameter can be obtained by agglomeration without using a chemical additive, such as an electrolyte.
In the case where agglomeration is effected by heating, the method can further comprise an aging step subsequent to the agglomeration step. The aging step is described in more detail below. The agglomeration step and the aging step are effected sequentially and, therefore, the boundary between these processes is not necessarily clear cut. However, a process wherein a temperature range of from (Tgxe2x88x9220xc2x0 C.) to Tg is maintained for at least 30 minutes is defined herein as an agglomeration step.
The agglomeration temperature is preferably a temperature at which toner particles having a desired particle diameter are formed, by keeping the mixture for at least 30 minutes at the given temperature. To reach the given temperature, temperature can be elevated at a constant speed or stepwise. The holding time is preferably from 30 minutes to 8 hours, more preferably from 1 hour to 4 hours in a temperature range of from (Tgxe2x88x9220xc2x0 C.) to Tg. Thus, a toner having a small particle diameter and sharp particle size distribution can be obtained.
In the process of the present invention, the particulate resin and/or particulate charge control agent can each, independently, be added to the process before or during the agglomeration step, between the agglomeration step and aging step, during the aging step or after the aging step. Further, if either component is added after the aging step, a second aging step can be performed if desired, under the same conditions noted above for the aging step.
In the case where agglomeration is effected by use of electrolyte, the electrolyte can be combined with a mixed dispersion of primary polymer particles, colorant particles, and optionally other components. Suitable electrolytes can be organic salts or inorganic salts. A monovalent or polyvalent (divalent or more) metal salt is preferable. Specifically, mention may be made of NaCl, KCl, LiCl, Na2SO4, K2SO4, Li2SO4, MgCl2, CaCl2, MgSO4, CaSO4, ZnSO4, Al2(SO4)3, Fe2(SO4)3, CH3COONa and C6H5SO3Na.
The amount of electrolyte to be added varies depending on the particular one chosen, and is, in practice, used in an amount of from 0.05 to 25 parts by weight, preferably from 0.1 to 15 parts by weight, more preferably from 0.1 to 10 parts by weight based on 100 parts by weight of the solid content of mixed dispersion used (wherein the mixed dispersion comprises, at least primary polymer particles and colorant particles).
If the amount of electrolyte to be added is significantly smaller than the above-described range, various problems tend to occur. Namely, the agglomeration reaction proceeds so slowly that finely divided particles having a diameter of not more than 1 xcexcm are left behind after the agglomeration reaction or the average particle diameter of the aggregates of particles thus obtained is not more than 3 xcexcm. Further, if the amount of electrolyte added significantly exceeds the above-described range, various other problems also can occur. Namely, the agglomeration reaction may proceed too rapidly to control. The resulting agglomerate of particles contains coarse particles having a particle diameter of not less than 25 xcexcm or have an irregular amorphous form.
Further, in the case where agglomeration is effected by adding an electrolyte, the agglomeration temperature is preferably in the range of from 5xc2x0 C. to Tg.
As noted above, in order to enhance the stability of the aggregates (toner particles) obtained in the agglomeration step, an aging step (causing the fusion of agglomerated particles to each other) at a temperature of from Tg to (Tg+80xc2x0 C. or more), preferably (Tg+20xc2x0 C.) to (Tg+80xc2x0 C.), but below the softening point temperature of the primary polymer particles may be preferably added. The addition of the aging step makes it possible to substantially round the shape of the toner particles or control the shape of the toner particles. This aging step is normally performed for a time of from 1 hour to 24 hours, preferably from 1 hour to 10 hours.
The agglomeration step can be performed in any suitable apparatus, but is preferably performed in a reaction tank with agitation. Substantially cylindrical or spherical reaction tanks are preferably used. When the reaction tank is substantially cylindrical, the shape of the bottom thereof is not particularly limited. However, generally a reaction tank having a substantially circular bottom is preferably used.
In order to improve agitation efficiency, the volume of the mixed dispersion is preferably xc2xe or less, preferably ⅔ or less of the volume of the reaction tank. When the volume of the mixed dispersion is significantly smaller than that of the reaction tank, the dispersion bubbles violently, increasing the viscosity. As a result, coarse particles tend to be formed, agitation sometimes cannot occur effectively depending upon the shape of an agitating blade, and, the productivity is lowered. Thus, the above-described volume ratio is preferably {fraction (1/10)} or more, more preferably ⅕ or more.
As an agitating blade to be used in the agglomeration step, any agitating blade can be used, such as conventionally known commercially available agitating blades. Suitable commercially available agitating blades, include anchor blades, full zone blades (produced by Shinko Pantec Co., Ltd.), Sunmeler blades (produced by Mitsubishi Heavy Industries, Ltd.), Maxblend blades (Sumitomo Heavy Industries, Ltd.), Hi-F mixer blades (produced by Souken Kagaku K.K.) and double helical ribbon blades (produced by Shinko Pantec Co., Ltd.). A baffle may also be provided in the agitating tank if desired.
Generally, the agitating blade is selected and used depending upon the viscosity and other physical properties of the reaction liquid, the reaction itself, and the shape and size of the reaction tank. Such selection is within the skill of the ordinary artisan. As a preferred agitating blade, however, specific mention may be made of a double helical ribbon blade or anchor blade.
The toner according to the present invention can be used together with one or more other additives such as a fluidity improver as desired. Specific examples of such fluidity improvers include finely divided hydrophobic silica powder, finely divided titanium oxide powder and finely divided aluminum oxide powder. The fluidity improver is, when present, normally used in an amount of from 0.01 to 5 parts by weight, preferably from 0.1 to 3 parts by weight based on 100 parts by weight of the binder resin used.
Further, the toner according to the present invention may contain an inorganic particulate material such as magnetite, ferrite, cerium oxide, strontium titanate and electrically conductive titania or a resistivity adjustor or lubricant, such as styrene resin or acrylic resin, as an internal or external additive. The amount of such an additive to be added may be properly predetermined depending on the desired properties. In practice, however, it is preferably from 0.05 to 10 parts by weight based on 100 parts by weight of the binder resin used.
The toner of the present invention may be in the form of either a two-component developer or a non-magnetic one-component developer. The toner of the present invention, if used as a two-component developer, may have any known carrier such as magnetic materials (including iron powders, magnetite powders, ferrite powders,) materials obtained by coating the surface of such a magnetic material with a resin and magnetic carriers. As the coating resin to be used in the resin-coated carrier there may be used generally known resins, such as styrene resin, acrylic resin, styrene-acryl copolymer resin, silicone resin, modified silicone resin, fluororesin or mixture thereof.
The toner of the present invention produced by using the above-described respective components, comprises a resin wherein at least one of primary polymer particles or particulate resin are crosslinked. When a crosslinked resin is used, the THF insoluble content is high. When an uncrosslinked resin is used, it is substantially dissolved in THF. Generally, the colorant is not THF soluble. Further, although the charge control agent is sometimes THF-soluble and sometimes THF insoluble, the charge control agent is used in a small proportion compared with the other components. By taking these facts into consideration, the THF insoluble content of the toner of the present invention is controlled in a range of from 15 to 80 w/w %. The tetrahydrofuran insoluble content is preferably 20 w/w % or more, and is preferably 70 w/w % or less.
In the toner of the present invention when both primary polymer particles and particulate resin are crosslinked, which is a most preferred embodiment of the present invention, the THF insoluble content of the toner is 20 to 70 w.w %, preferably 30 to 70 w/w %.
The THF insoluble content of the binder resin contained in the toner is preferably from 10 to 70% by weight, more preferably from 20 to 60% by weight.
Further, though it depends on the monomer composition of the primary polymer particles and the particulate resin, the THF insoluble content of the binder resin contained in the toner tends to be lower than the THF insoluble content of the primary polymer particles, particularly in the case of preparing the toner using an aging or fusion-bonding step (i.e. the primary particles become at least partially fused).
The toner of the present invention further comprises wax having a melting point of 30 to 100xc2x0 C. The content thereof in the toner is preferably 1 part by weight or more, more preferably 5 parts by weight or more and particularly preferably 8 parts by weight or more to 100 parts by weight of a binder resin of the toner (wherein the term xe2x80x9cbinder resinxe2x80x9d is used herein to mean the sum of the resin constituting primary polymer particles and the resin constituting particulate resin, as described earlier). The wax content is also preferably 40 parts by weight or less, more preferably 35 parts by weight or less and most preferably 30 parts by weight or less.
When the toner of the present invention is used in a printer or a copying machine having high resolution, the toner preferably has a relatively small particle size and has a sharp particle size distribution for attaining a uniform charged amount in respective toner particles.
The average volume particle diameter of the toner of the present invention is preferably 3 to 12 xcexcm, more preferably 4 to 10 xcexcm, particularly preferably 5 to 9 xcexcm. As an index representing particle size distribution, the ratio of volume-average particle diameter (DV) to number-average particle diameter (DN), i.e., ((DV)/(DN)) is used. The present invention toner preferably has a (DV)/(DN) of 1.25 or less, more preferably 1.22 or less and most preferably 1.2 or less. The minimum (DV)/(DN) is 1, which means that all particles have the same particle size. This is advantageous in the formation of an image having a high resolution. Practically, however, a particle size distribution of 1 is extremely difficult to be obtained. Accordingly, in view of production considerations, (DV)/(DN) is preferably 1.03 or more, more preferably 1.05 or more.
When finely divided powder (toner having excessive small particle diameter) is present in too high an amount, blushing of a sensitizing body and scattering of toner into the inside of an apparatus are likely to occur and the charged amount distribution is also liable to be worse. When coarse powder (toner having excessive large particle diameter) is present in too high an amount, the charged amount distribution is liable to be worse, which is unsuitable for forming a high resolution image. For example, when the toner has an average volume particle diameter of 7 to 10 xcexcm, the amount of toner having a particle diameter of 5 xcexcm or less is preferably 10% by weight or volume or less, more preferably 5% by weight or less of the entire amount of the toner. The amount of toner having a particle diameter of 15 xcexcm or more is preferably 5% by weight or volume or less, more preferably 3% by weight or less.
When such a toner having a relatively small particle diameter and a sharp particle size distribution is produced, the production method according to the emulsion polymerization agglomeration method of the present invention is advantageous compared with suspension polymerization or kneading-pulverizing method.
The 50% circular degree of the present toner is preferably 0.95 or more, more preferably 0.96 or more. (circular degree=circumference length of circle having the same area as that of projected area of particle/circumference length of projected image of particle)The maximum 50% circular degree is 1 which means that the toner is substantially spherical. However, such a toner is difficult to be obtained. Thus, in view of production considerations, it is preferably 0.99 or less.
The toner of the present invention will be further specifically described below in terms of several preferred embodiments.
A first preferred embodiment is a toner wherein particulate resin is adhered or fixed to an agglomerate of particles obtained by agglomerating at least primary polymer particles and primary colorant particles; the THF insoluble content of the primary polymer particles is from 15 to 70 w/w %, preferably from 20 to 70 w/w %; the THF insoluble content of the particulate resin is from 5 to 70 w/w %, preferably from 10 to 70 w/w %; and the toner includes a wax having a melting point of from 30 to 100xc2x0 C.
A second preferred embodiment is a toner wherein particulate resin is adhered or fixed to an agglomerate of particles obtained by agglomerating at least primary polymer particles and primary colorant particles; the THF insoluble content of the primary polymer particles is from 15 to 70 w/w %, preferably from 20 to 70 w/w %; the particulate resin is not crosslinked; and a wax having a melting point of 30 to 100xc2x0 C. is included in the toner.
A third preferred embodiment is a toner wherein particulate resin is adhered or fixed to an agglomerate of particles obtained by agglomerating at least primary polymer particles and primary colorant particles; the primary polymer particles are not crosslinked; the THF insoluble content of the particulate resin is from 5 to 70 w/w %, preferably from 10 to 70 w/w %; and a wax having a melting point of 30 to 100xc2x0 C. is included in the toner.
Among these three preferred embodiments, as primary polymer particles, those obtained by emulsion polymerization using particulate wax having a melting point of 30 to 100xc2x0 C. as seed are more preferably used.
Further, also among these three preferable embodiments, the THF insoluble content of the primary polymer particles and that of the particulate resin are each most preferably from 15 to 70 w/w %.
Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.